Two-way wave transmission system



June 14, 1927. 1,632,282 J. F. FARRINGTON TWO-WAY WAVE TRANSMISSION SYSTEM Filed Dec. 29. 1923 outrun sraT -s "Parent; car es.

JOE-111T FARRINGTON, F FLUSHING', NEW YCRK,"ASSTGNQR T0 WESTERN ELECTRIC COMPAIIY, INCORPORATED, OF NEW YORK, N. Y}, A CORPORATION 01" NEW YORIL:

TW'O-XVAY R AVE TRANSMISSION SYSTE'EI.

Application-filed December 2 accomplished by varying the frequency of the transmitted carrier by an audible amount in accordance witha telegraph code and thereby varying the'detected difference frequency accordingly. A local receiver source, producing waves of the normal diffr ence frequency is used. Waves from this source are combined with the detected diffcrcncc frequency wave. When telegraph signals are being sent the combination wave contains a component having a frequency equal to the change in carrier frequency. An indicator is placed across the output of the combining device. When no telegraph signal is being sent there is no wave impressed on the indicator or in other words the frequency is zero. When the incoming or outgoing'carrier is changed to transmit telegraph impulses there is a tone impressed on the indicator. The telegraph channel of the system of my said application'operates, therefore, in a mannersimilar to that of the Farrington or difference frequency method, and the operation as in that method,

is characterized by reception of both the distant and local telegraph signals in the telegraph receiver. However, if simultaneous all duplex telegraphy were attempted the telegraph beat frequency would be a composite of the telegraph. frequencies transmitted simultaneously from both stations; that is, the telegraph messages would be superposed and render simultaneous duplex transmis. sion impracticable.

in accordance with the present invention means is provided in association. with the circuit arrangement of my said application whcrely thev frequency of the local teleg iph source is made to vary with the variations of outgoing carrier frequency during telegraph transmission, whereby the side tone is eliminated and. since this arrange; inent removes the effectin the teleg 'aph res, 1923. sci-mine. esa,eo5.-

only. Therefore, the receiving operator can hear in his receiver the incoming telegraph message, only andQmay receive this message and simultaneously transmit a ,message without the slightest interferencebetween the oppositely directed transmissions.

The single figure of the drawing illustrates a system embodying one form of the invention. i

Referring to the drawing, a constant cur rent modulating system 1, having an oscillator O of welldrnown type, is shown arranged for radio telephone transmission. The modulation system is of the type dis closed in U. S. Patent to R. A. I-leising No.

1,537,941, May 19, 1925, although other systems of modulation could equally well be used. The antenna is broadly tuned to the frequency f, of the oscillations produced by oscillator O and therefore serves to'transmit oscillations of frequencies ,f iS and 7",, representing, respectively, the side" bands and the unmodulated carrier component of speech modulated outgoing carrier waves. The frequency of the speech waves at this station is represented by 55,,- change the carrier. frequency f, for code signaling a key K is provided to operate a relay 4L which at its left armature short circuits a reactance R in the frequency determining circuit of the oscillator O to. vary. the carrier frequency by an audible amount, for example,,150 cycles.

The distant station,,not shown, hassimi lar transmitting apparatus, exceptethat its oscillator produces waves of. frequency f, and accordingly transmits to theetation shown oscillations of frequencies his, and f representing, respectively, the modulated side bands and unmodulated carrier frequency component, S, denoting the frequency ofspeech waves to be transmitted from the distant station. The frequencies- 5', and f, differ by an .a-mount'preferablyin the range above. good audibility. In order efficiently to select and receive the incoming waves, the an'tennais provided with an additional path d tuned, in conjunctionMiththe transmitting antenna circuit, to the mean frequency of the received waves. This path includes a loop E anti-resonant atthelfrequency t, and accordingly passes little cur- In order to inaudible difference or. intermediate frequency component is modulated by Wavesof frequency S and during incoming: speech transmission by Waves of frequency S In the operation of the circuit, speech current of frequenciesfran'ging substantially from 200 to 2000 cycles is transmitted by talking into the transmitter S which modulates the radio frequency outgoing carrier wave by means of the constantcurrent modulator s'ystenrh I. A tone telegraph signal may be sent by operating thekey K This impresses onto the modulator from I source G" atone of frequency outside the speech frequency range, for example, about 2500'cycl'es. The'tone may be'ofless ampli tude than the speech signal and will, therefore, require less energy. The modulator has, as nearly as may be practical, a linear characteristic so that there will be little or no cross modulation of the speech bythe tone. Atbotlr local and distant stations the circuit D of the receiver is arranged to pass the intermediate frequency and its speech and" tone telegraph side bands, the frequen cies of which. are shifted up and down 150 cycles due to the telegraph signal sent by key K. The intermediate frequency side a hands extend 2500 cycles above and below the frequency of" the intermediate carrier Whenthe 2500' cycle telegraph tone used; and extend only 2000' cycles when the telephone channel alone is in operation. Both local and distant speech and tone telegraph will be heard in the outputj of intermediate frequency detector I FD No, 1. Thecircuit l h which may be' a low pass filte'r with cut -off at O0-cycles,selects speech waves S; and S; anchpasses; them to'the headset 8. The tele graph toneisselected by circuit Htfwhich may be a pair of resonant coupled circuits,

ahighpass filter cutting off frequencies helowg for example, 2300 cycles, or a band pass filter, selecting a frequency of OO cycles;

and passed onto the head phone G1. By

using slightly different tones, say- 24LOO cycles for the distant station and2500'for the cur-f rent from source Ur at the' local station, 7 simultaneous: tone telegraphy" could be acrcomplished bythe use of suitable selective circuits at H to pick outthe distant sta-j tion" tone and exclude the local telegraph tone." If intermodula'tion in the process of detection occurs" between the tones'and of key K does not necessitate the use of additional' radiated energy over and above that normally used for telephony while the trans mitter is use for telephony and is transmitting a carrier wave. The frequency of the transmitter oscillator O is changed when key K- is closed as described but this change in carrier current does not interfere with the previously mentioned speech or tone telegraph reception, circuit D being made to pass a band of frequencies wide enough to allow for a 1 cycle shift inthe intermediate" frequency range. The signal due to the actuation of key K is not received at the station of origin because the local intermediate frequency oscillator U has its fre quency shifted 150 cycles in the same direction as the transmitter frequency due to the closure of a short circuit about a reactance R, by the right armature and front contact of'relay l. WVhen the carrier at the distant stationis changed 150 cycles, however, there is resultant 150 cycle tone in the second intermediate frequency detector I'FD No, 2' of the local station. Circuit T selects the intermediate frequency carrier and is designed to'prevent the transfer of speech and tone telegraph signals. Low pass filter V cuts oifat" frequencies above, for example 170 cycles, or maybe a circuit resonant at 150cycles. VA signalwill occur in the head set W onlyw'hen the distant station sends with its key corresponding to K which changes the carrier by 150 cycles, since in such case relay 4; at the local receiving stap ti'onis not operated and reactan'ce R is not short circuited. a

The telegraph channel controlled by key K may beomittedfrom the system ormay', at any time, be left inactive without in any way affecting the effectiveness or the teie graph channel controlled by key K or the telephone channel, each of which maybe worked full duplex.

The novel featureshelieved to be inherent in" the invention aredefine'd in the'app'ended 1. duplex"wayetransmission system,

other waves, the method or signaling which 7 comprises producing I frequency changes in the outgoing Waves to produce signals, heating waves of frequency controlled by incoming waves with locally produced waves to produce waves of different frequencies to produce signals, and preventing side tone by causing equal and simultaneous changes in the outgoing and local waves.

3. The method which comprises combining wave energies to produce a waveenergy of beat frequency and at intervals producing equal and simultaneous changes in the fre quencies ot the combined energies and in such directions as to n ajintain the beat frequency constant.

4. In a signaling system, means for preventing the productiim of local indications a result of signaling changes of frequency in outgoing waves which comprises means for producing signaling changes of frequency in outgoing waves, means which tends to be responsive to said frequency changes for producing a local wave having a frequency corresponding at all times to said changes, and means for producing simultaneously therewith such'changes in the system as will prevent the operation of said responsive means whereby the production of said local wave is prevented 5, The method of duplex telegaphy between two stations which comprises producing a signal carrier wave at one station, changing the frequency of said wave in accordance with telegraph niessagei'i, transmitt ng said changed frequency wave, simultaneously performing a corresponding series of operations at the other station, translating, at each station, the message bearing wave from the other station into an audible frequency wave having message characteristics by steps involving beating said received frequencies with a portion of the locally-produced wave used for transmission, and pre'\ 'enting the message characteristic in said locally-produced wave from affecting the character of said audible frequency wave.

6. The method which comprises produclog a carrier wave modulated in amplitude in accordance with two independent messages, and varied in frequency in accordance with two other independent messages, and selectively simultaneously deriving from said wave and receiving without interfering one with the other at least three of said messages.

7. The method of high frequency signalfrom additional source, and detecting said beats and the method of transmittino which consists in changing the frequency'of the locally produced wave in correspondence with the change in the normal carrier fi' quency;

9. in the metl'iod of simultaneous tel-ephony and tel-egraphy in which tiephonic si nals are transmitted as modulations of a carrier frequency wave, and in which teleg aphic sic als are 'lwansinitted by changing equency of said wave by an the car: audibli amount, the method of reception and transmission which comprises. receiviug the telephonic signals by demodulating a portion of the received energy, and receiving the telegraphic signals by coml;iin--- ing a portion of the received wave with a locally produced wave, the frequency of which differs from the normal carrier by an inaudible amount, detecting said combined waves, selecting from the detected wave the 'fl6(]lil-12(i con'iponent co spending to the 'dilferenre between the carrier and local frequencies, and stepping down by a non-signaling wave said dilferonce frequency to the value corresponding to the change in carrier frequency at the remote station, and changing the frequency of the non-signaling wave in correspondence with the change in the carrier frequency during transmission.

10. The method of two-way signaling which comprises continuously transmitting in opposite directions between two communicating stations two high frequency waves differing by an inaudible frequency, combining at. each station the received wave with a portion of the transmitted wave from the same station to give an auxiliary difference fre uenc wave, chan 'in the frey e e quency of the transmitted wave at either station by an audible amount in accordance with a signal, detecting said signal at the ther station by combining the changed auxiliary frequency wave resulting from said signaling operation with a locally produced wave having'a frequency equal to the auXiliary frequency during, nonsignaling operation, separating from the product of the combining operation the audible freopuency component which is present when signals are being transmltted trom the distant station, and changing the he 7 quency of thelocally produced wave at the transmitting station for changing the car transmitting station to correspond with the changein the high frequency transmitted wave.

11. In a two-way signaling system, means at each. station for transmitting a carrier wave, means at each station for producing an additional carrier wave, means at the rier Wave to transmit signals and for correspondingly changing the frequency of the additional wave theil-eat, means at the receivin station torproducinp' from the transmittecl carrier wave a wave having corresponding signal frequency changes, and means at the receiving station for detecting the beat frequency of said received carrier waveand the unchanged additional wave thereat.

12. A two-way signal transmission system comprising two communlcating stations each of which comprises, in combination. a

source of high frequency waves means for changing the frenquency of said source, a transmitting circuit resonant to said frequency, a receiving circuit resonant to a frequency (littering from said first mentioned frequency by an inaudible amount, means for combining a portion of the trans mitted energy with energy received from the other station to produce an intermediate frequency wave, a local source of high frequency waves related to said combining means, additional means related to said comhining means and said local source and adapted to derive from the currents associated therewith an audible frequency current during the intervals of changed carrier frequency, and means actuated at the transmitting station for simultaneously chang ing the frequency of said local source to correspond with said change in carrier frequency.

13. The method of signaling between two stations which comprises generating a car rier Wave at each of said stations, produc- 'ing amplitude modulations in each of said waves in accordance with an independent message, varying each of said carrier waves in frequency in accordance with one other independent message, and selectively simultaneously deriving from said waves and re- 'slectively simultaneously deriving from said carrier wave and receiving without interfering one with the other at least three of said messages.

In witness whereof, I hereunto subscribe my name this 22 day of December A; 1)., 1923.

JOHN F. HARRINGTON. 

